Radio receiving system



C. W. RICE RADIO RECEIVING SYSTEM Aug. 30,1927. A 1,640,427

Filed Nov. 21. 1922 lnv e wnorfl chesnerw RI ce- MXW Hi5 Attornet Patented Aug. 30, 1927.

UNITED STATES CHESTER W. RICE, OF

SCHENEGTADY, NEW YORK, ASSIGNOR T0 GENERAL ELE TRIO COMEANY, A CORPORATION OF NEW YORK.

RADIO runcnrvrns SYSTEM.

Application filed November 21,1922 Serial No. 602,427.

The object of my invention is to provide a method of and apparatus radio reception which will be particularly adapted to;

prevent interference from stations employing wave lengths close to those which it is desired to receive.

In radio reception it is frequently'desired to receive signals from distant stations at the same time that other stations are operating on wave lengths close to those of the station from which it is desired to receive. If the undesired station is far enough distant from the receiving station so that the received signals are of the same order of magnitude as the desired signals, interference may be eliminated by careful tuning, but even in this case difficulties arise because of the large number of radio broad: casting stations which operate upon prac tically the same wave length.

As the magnitude of the signals received from the undesired stations increases in proportion to that of the desired signals the difficulty of preventing interference increases until apoint is reached where it is practically impossible by ordinary tuning methods to eliminate the signaling impulses received from a nearby station and receive signals from a distant station. I

In order to permit of reception under circumstances where ordinary tuning meth ods become ineffective, I provide at the receiving station an artificial transmission line having an effective length equal to several wave lengths of the slgnals to be received.

I impress the received signaling impulses upon this transmission line and provide means for coupling a receiving set to this transmission line at two different points one of which will be located at or near the end of the line upon which the received impulses are impressed and the other at a point along the length of the line near the extreme end.

If it is assumed that the interfering imulses are in phase with desired impulses at the end of the transmission line upon which the impulses are impressed therewill be a progressively increasing phase difference between the two impulses as they proceed along the transmission lines, the magnitude of this phase difierence of course depending upon the difference in wave length between the two impulses. The couplingmeans is therefore so arranged that at least one of the couplings may be moved along the transmisapparatus phase and therefore neutralized. If this sion line to such a point that the interfering impulses. are impressed upon the receiving by the two couplings in opposite point is several wave lengths distant from the receiving end'of the transmission line the desired impulsesimpressed upon the rcceiving apparatus will notbe in phase opposition and will therefore add vectorially in the receiving apparatus. If the transmission me is long enough or the difference inwave lengths great enough the desired impulses may be in phase at the selected'point so that they will add directly in the receiving apparatus.

The invention will best be understood by reference to the following description taken in connection with the accompanying drawingin which Figs. 1 and 2 show diagrammatically two different systems for carrying out my invention.

As indicated in the drawing, I provide an artificial line 1, which may be inductively coupled to the antenna 2, as in Fig. 1, or directly coupled thereto, as indicated in Fig. 2. In the arrangement shown in Fig. 1 the transmission line is open ended so that reflection will occur and the forward moving wave will interfere with the reflected wave to form nodes and antinodes. Near the reflection point the desired wave and the interfering wave are practically inseparable, but as we move back along the line a point will be found where the interfering wave has an interference node while the desired signal is of full strength. A coil 3 is provided which is coupled to the artificial line near the reflection point and a coil 4: is provided which is coupled to the artificial line near the point at which the undesired signal has the opposite phase. By adjusting the positions of the two coils the interfering signal may be neutralized in the receiving set 5. The principal effectof sliding the coil 3 along the transmission line is a variation in intensity and the proper phase adjustment maybe obtained by movement of the coil 4. When the adjustment is correct for neutralization of the undesired impulses the desired signals will not be neutralized because of the fact that at the coupling point of'coil 3 the interfering and desired signals are approximately in phase while at the coupling point of coil 4: they are not in phase.

With this arrangement, I have found it possible at a point within two miles of a powerful broadcasting station to prevent interference therefrom and receive sig nals from broadcasting stations several hundred miles distant operating on closely adjacent wave lengths.

In the arrangement shown in Fig. 2 the end of the artificial transmission line is damped by a resistance 6 equal to the surge impedance to prevent reflection. Assuming that at the coupling point of coil 4L the desired and interfering signals are in phase a point may be found for coupling coil 3 where the interfering wave is in phase'opposition with the interfering wave at coupling coil 4:, and therefore can be balanced out by adjustment of the intensity coupling of coil 4. Under these circumstances the desired signal has a dii'l erent phase relation at the points 3 and 4:, and will not be balanced'out.

In 1 I have indicated the output circuit of the receiving set 5 as regeneratively connected to the antenna to compensate for losses introduced by the transmission line while in Fig. 2 I have shown the regenerative connection to the grid circuit of the receiving set 5. Either of these methods of re generation may be employed with both forms of transmission line. In case it is desired to eliminate more than one interfering station additional coupling coils to the artificial line may be provided to neutralize impulses re ceived from the additional interfering stations.

lVhile I have shown and described the preferred embodiments of my invention it will be apparent that many modifications of the connections employed, and in the manner of operating the system may be made without departing from the scope of my invention as set forth in the appended claims.

Nhat I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination in a radio receiving system of an artificial transmission line having an effective length equal to several Wave lengths of the signals to be received, means for impressing received signaling impulses upon said artificial line and a receiving set having an input circuit coupled to said artificial line at two different points alon its length at least a wave length apart.

2. The combination in a radio receiving system of an artificial transmission line having an effective length equal to several wave lengths of the signals to be received,

-1neans for impressing received signaling impulses upon said artificial line, and means for couplingthe input circuit of a receiving set to said artificial line at two different points along its length, said means being adjustable to permit the selection of two separated coupling points where the phase relations between desired signaling impulses and interfering impulses of neighboring frequency will be materially difierent.

3. The combination in a radio receiving system of an artificial transmission line having an effective length equal to several wave lengths of the signals to be received,

means :for impressing received signaling impulses upon said artificial line, and means for coupling the input circuit of a receiving set to said artificial line at tWo difiierent points along its length, said points being so chosen that interfering impulses of neighboring frequency will be of opposite phase at the two points and will therefore be neutralized in the receiving apparatus while the desired signaling impulses will add in the receiving apparatus.

4. The method of operating a radio receiving system comprising an artificial trans mission line and a receiving apparatus which consists in impressing received signaling impulses upon the artificial line and impressing impulses upon the receiving apparatus from' two different points in said artificial line at least a wave length apart.

5. The method of operating a radio receiving system comprising an artificial transmission line and a receiving apparatus which consists in impressing received signaling impulses upon the artificial line and impressing impulses upon the receiving a'pparatus "from two different points in said artificial line so chosen that the phase relations between the desired signaling impulses and interfering impulses of neighboring frequency will be materially different at the two points.

6. The method of operating a radio receiving system comprising an artificial trans mission line and a receiving apparatus which consists in impressing received signaling pulses upon the artificial line and impressing impulses upon the receiving apparatus from two different points in said artificial line at least a wave length apartso chosen that interfering impulses of neighboring frequency will be impressed in opposite phase and hence neutralized in the receiving apparatus while desired signaling impulses will add in the receiving apparatus.

In witness whereof, I have hereunto set my hand this 20th day of November, 1922.

CHESTER WV. RICE. 

